1. Field of the Invention
The present invention relates to a fuel injection control system for an internal combustion engine and more particularly to a control system for improving the starting performance of an internal combustion engine.
2. Description of Related Art
Conventionally, it is known to inject a relatively large amount of fuel at a timing which is not synchronous with a suction stroke, as a fuel injection control carried out when an internal combustion engine is started. Fuel evaporated before the suction stroke is sucked into cylinders and is burned, thereby starting the internal combustion engine. By increasing the fuel injection amount, the fuel (fuel evaporated and sucked into the cylinders) necessary for the start-up is assured.
It is also known, because the evaporation amount of fuel changes depending on the engine temperature (cooling water temperature), to correct the fuel injection amount at the time of starting in accordance with the cooling water temperature.
Further, Japanese Examined Utility Model Publication No. 1-21156 proposed to improve the starting performance of an internal combustion engine, to learn the relation between the fuel injection amount at the time of engine starting and a time actually required for start-up, and to increase or decrease the fuel injection amount at the time of the next engine starting, on the basis of the learned result, so as to reduce the starting time.
At the time of so-called cold engine starting which is a start-up when the engine temperature is low, however, an evaporation amount of fuel is small and even if the fuel injection amount is increased, and a misfire occurs. There is consequently a problem that exhaust emission gets worse.
It is a first object of the invention to provide a fuel injection control system of an internal combustion engine, which can improve the starting performance of the internal combustion engine and can especially improve the starting performance during cold engine starting.
It is a second object of the invention to provide a fuel injection control system of an internal combustion engine that can shorten the starting time of the internal combustion engine.
According to the present invention, a fuel atomization device is provided to atomize fuel injected at the time of engine starting. The fuel atomization device may be a type that increases fuel pressure to a higher value at the time of engine starting than after the engine starting. Alternatively, the fuel atomization device may be a type that supplies assist air to the injected fuel.
Preferably, an intake valve is opened for a longer period at the time of engine starting than after the engine starts, so that more fuel may be supplied to an engine cylinder.
Preferably, a fuel leakage which may occur during engine stop is estimated, and the amount of fuel to be injected at the time of next engine starting after the engine stop is corrected by the estimated amount of fuel leakage.
Preferably, a change in the cylinder pressure between the compression stroke and the combustion stroke is calculated, and the fuel injection at the time of engine starting is corrected by the cylinder pressure change.
Preferably, fuel injection timing at the time of engine starting is retarded relative to that of post-engine starting.
Preferably, the amount of injected fuel adhered to an intake port and not supplied into an engine cylinder after the closing of an intake valve is estimated, and the amount of fuel to be injected next is corrected thereby.
Preferably, the amount of fuel is divided into two fuel injections at the time of engine starting, in the event that it is too large to be injected at one time relative to the opening period of an in take valve.
Preferably, the amount of intake air supplied for an engine idle speed control is reduced at the time of engine starting, so that air-fuel mixture is enriched in fuel.